This invention relates to a method of producing a shaft having plate-like members joined thereto and, more particularly, to a cam shaft for driving valves of an internal combustion engine, which cam is made of hard material excellent in wear resistance and which shaft is rigid and lightened in weight.
As a conventional method of lightening the weight of a cam shaft and improving the wear resistance of the cam, a method of joining a pipe made of steel and other parts by brazing is disclosed in Japanese Patent Laid-Open No. 54-86456. According to this method, both parts constituting the cam shaft and jigs made of refractory material are inserted in a high-temperature atmosphere furnace to join the parts by brazing, so that large equipment therefore is necessary, and the method is poor in workability and is not conducted economically.
A method of joining a cam and a hollow shaft by inserting the hollow shaft of steel in a cam and expanding the hollow shaft is disclosed in Japanese Patent Laid-Open No. 60-151459. According to this method, stresses are applied over the whole of the hollow shaft, so that there is a fear that the cam is broken. Further, precision, particularly, rectangularity and parallelity after joining the cam and the shaft and positional precision of the cam relative to the shaft are not sufficient. Japanese Patent Laid-Open Nos. 60-152665 and 59-176407 are relevant to this kind of art.
Further, there is Japanese Patent Laid-Open No. 54-102209 in which a cam is made of wear-resistant iron base sintering alloy, and the cam is joined to a shaft by a material of liquid phase produced by the sintering alloy. According to this method, the cam is assembled to the shaft in a high-temperature atmosphere, so that precision of the assembled cam and shaft is not sufficient.